Get the timestamp for the first day (monday) of a week number

// Offset: numeric weekday of January,
// 1st in given year (e.g. 'Donnerstag' => 4)
$offset = date('w', mktime(0, 0, 0, 1, 1, $weekNumber);
 
// Calculate timestamp of monday from above offset
$offset = ($offset < 5) ? 1-$offset : 8-$offset; $monday = mktime(0, 0, 0, 1 , 1+$offset, $weekNumber);   // Finally: calculate timestamp of monday in requested week return strtotime('+' . ($dateArray[1] - 1) . 'weeks',                  $monday);